Apparatus for electrolytic cutting, shaping and grinding



Oct. 17, 1961 G. FQKEELERIC 3,

APPARATUS FOR ELECTROLYTIC CUTTING, SHAPING AND GRINDING Original Filed Sept. 18, 1952 2 h sh 1 110 115 1 g JIM INVENTOR.

2w v m w ww Oct. 17, 1961 G. F. KEELERIC 3,004,910

APPARATUS FOR ELECTROLYTIC CUTTING, SHAPING AND GRINDING 2 Sheets-Sheet 2 Original Filed Sept. 18, 1952 g 174 H U u fii i7 INVENTOR.

uuuuu u an United States Patent 100,493 7 Y 8 Claims. Cl. 204-228) My invention relates to apparatus for electrolytic cutting, shaping, and grinding of very. hard materials.

. This application is a division of my copending application Serial No. 310,244, filed September 18, 1952, now Pat. No. 2,826,540.

With the increased use of very hard materials in the form of alloys or in the form of sintered carbides like tungsten carbide in the making of tools and dies, turbine buckets, ordnance, etc., the problem of economically cutting shaping, and grinding such materials is assum ing great importance. The common method of performing such operations (which I will refer to generally hereinafter as shaping) is by the use of diamond abrasive wheels, flat or contoured as may be required. Diamond abrasive wheels are costly and the diamond bort used in their manufacture threatens to become very scarce in the face of its increased usage.

Among the objects of my invention are the following:

To shape hard materials with accurate control of dimensions, fine finishing, freedom from heat stressing or cracks or checks, and with minimum loss through defects; 1

To carry out such shaping operations at high speed, safely, at low cost, and with a very low rate of wear on grinding wheels or cathodes used in the process;

To provide apparatus which may be readily adapt able to the large quantity of costly grinding equipment already in use;

To achieve the above results, it is my purpose to provide improvements in the electrolytic removal of material which may be augmented by the mechanical removal of insulating oxide films on the material to be shaped which interfere with electrolytic action. Where very high rates of removal are'des iredI augment electrolytic action by abrasive action.

Another purpose of my invention is to provide control of the degree of sparkingor arcing which occurs between the work to be shaped and the shaping electrode.

While the general phenomenon of electrolysis is well known, theiprinciple has not heretofore been found ap plicable to the shaping of hard materials. Part of the reason for this fact lies in the slow removal rate provided .by ordinary electrolytic methods, and part of the reason lies in the difficulty of getting accurate and smooth surface control, These are serious problems, for a practical method of shaping requires removal rates several hundred times greater than those encountered in such processes as electroplating and control of the surface on which removal is carried forward within a fraction of .001 inch.

If the attempt were made to increase the removal rate simply by increasing the voltage applied to the electrolytic circuit, the result would be to cause intolerable heating, gassing, and decomposition of the electrolyte, as well as the wasteful dissipation of a very large amount of electric energy. This would also result in uneven and uncontrolled removal of material so that the remaining surface would be of little use for industrial purposes.

If the attempt is made to increase the removal rate by obtaining higher current through reducing the space between the electrode and' the material to be shaped, then two additional problems arise.

The first is that if the gap is narrowed sufficiently to be useful, it is diflicult to replenish the electrolyte within the gap at a sufiiciently rapid rate. The second is that with a narrow gap there is likelihood of serious sparking or arcing between the electrode and the material through the electrotype. If heavy sparking occurs, it is likely to break over into arcing, and either the heavy sparking or arcing tends to produce a rough finish and damages the surface of the electrode. And in any case, the problem of maintaining adequately close spacing is diflicult, particularly in off-hand grinding where the tool is simply supported on a tool rest and moved by hand in order to bring about the desired shaping.

By the means I have devised, I am able to obtain a rate of material removal which is several hundred times the rates encountered in ordinary electrolytic processing. This may be illustrated by the fact that I am able to obtain current densities ranging from 200 amperes per square inch (of the surface of the material) up to more than 1000 amperes per square inch, whereas in ordinary electroplating, current densities will be of the order of l or 2 amperes per square inch. The rate of material removal is proportional to the current which is passed. At the same time, I am able to obtain a very smooth, even surface. The way in which I accomplish these results will be understood from the more detailed description of my invention which follows.

In the drawings,

FIG. 1 is a schematic representation of an embodiment of the mechanical apparatus used in my process, and a circuit diagram of the electrical system; and

FIG. 2 is an elevation, partly in section, of an arrangement for indicating and controlling the pressure urging the work piece against the moving electrode.

Referring to FIG. 1, I will explain first the mechanical system used in my invention.

The mechanical apparatus may include a wide variety of commonly used grinding equipment. In the drawings, a moving electrode 10 is mounted to a grinding shaft or spindle 11 through an electrically insulating bushing 13; The spindle or shaft may be driven by a motor 12, or in any other conventional manner.

The motor is mounted to a bed 14 which also carries a tool rest pedestal 15. This is arranged in such a Way that a tool to be ground may be rested on its upper surface and then moved by hand to achieve the desired shape. The tool proper frequently consists of a shank 17 to which a hardened tip 17a is attached, for example by brazing. The tip 17a is frequently made of a hard metalcarbide, such as tungsten carbide, while the shank 17 is made of steel. One important feature of my invention is that the tip 17a and the shank 17 are shaped together in one operation, and are shaped evenly, so that it is not necessary to work separately on the tip and the shank. The tool consisting of the shank 17 and its attached tip 17a may be mounted in any conventional way to a tool holder 16 which rests against the tool rest pedestal 15. It should be noted that good electric contact must be maintained between all of these elements-the tool, the tool holder, and the tool rest pedestal. Inasmuch as the electrolyte which is used is conductive and is necessarily splattered somewhat over this area, it is unnecessary to maintain polished surfaces, but the use of paint, etc., is to be avoided.

The arrangement of FIG. 1 for holding a tool in operative relationship to a moving electrode is suitable for off-hand grinding, but where a considerable number of identical tools is to be shaped, it is desirable to provide mechanical means for holding the tool with respect to the electrode. This mechanism is shown in FIG. 2.

Referring to FIG. 2, the electrode 10 has abrasive insulating spacers 40 mounted on its working surface. Elec- 3 trode is mounted to a rotating shaft 11 through an insulating bushing 13. On the bed of a grinding machine, I provide ways 42 on which is slidably mounted a shoe 44 having guides 44a. Within guides. 44: a tool holder 16 is slidably mounted.

Tool holder 16 is fitted with a clamp member 46, and a clamping bolt 48 by which the work piece17 with a hard tip 17a is clamped'in position.

.An air cylinder 50 is fastened by extending lugs 52 and bolts 54 to shoe 44.

Within the cylinder 50 is mounted piston 56 which is connected through piston rod 58 to tool holder 16 by pin 60. At the head of the cylinder is a small airbleed hole 62.

One of the guides 44a is provided with a boss 64 which carries a stud 65 to make connection to pitman 68 which is driven by a crank 7% in the conventional manner. The crank 70 may be turned by its own prime mover or may be linked through speed reducing. mechanism to motor 12.

The purpose of the crank mechanism and associated linkage is to give an oscillating motion to the work piece back and forth along the working surface of electrode 10. In some cases this is desirable in order that any wear, of the electrode 10 or insulating spacers 40 may be uniform across the working surface. V A flexible supply tube 72 isconnected to the head of cylinder 50. The air supply tube 72 is also fitted with a pressure gauge 74 and an adjustable pressure regulator 76 supplied from air supply line 78.

By setting the pressure regulator at the desired level, the amount of pressure urging the work piece 17 and 17a toward electrode :10 against insulating spacers 40 may be carefully adjusted and maintained. Ordinarily, for small work pieces, such as cutting tools, I prefer that the air cylinder be small, having a diameter of approximately one inch. The pressure regulator 76 may then V 4 Letters Patent 2,368,472 for Method of Making Abrasive Articles, issued January 30, 1945. If insulating spacer particles are'used which are less hard, then they maybe bonded to the electrode 10 and any irregularities in their protrusion may be eliminated by grinding with a fine abrasive wheel so that all of the particles protrude the desired uniform distance outwardly from the metal electrode 10.

With whatever arrangement is. used, care must be taken that a reasonable space is left between. the particles, and this space on the electrode must be electrically conductive. This means either that the bonding material used must itself be conductive, or that the presence of bonding material between the particles either be avoided at the time of application or removed by dissolving or etching, or in some other way, after; the particles have been applied. I prefer'not to occlude more than threefourths of the working surface of the metal electrode 1% thus assuring adequate metal surface to serve as an electrode in the electrolytic process. If the entire surface of the electrode is covered by abrasive, it must be sufiiciently pervious to provide channels for electrolyte adequate to carry the desired current. 1

The insulating spacers permit very close spacing, which is important not only in order to get requisite current densities, but also in controlling the dimensions and surface finish of the work. For example, if the space between the work piece and the moving electrode is opened upto as much as .005 inch, the surface gen be adjusted so as 'to supply very slight air pressure to the cylinder, thus putting very light force against the piston 56 so that the work piece makes firm but very light' contact with insulating spacers 40.

It should be understood that the work piece may be movable and the electrode may be fixed. Or, as in rotary grinding where the work pieceis circular in section, the work piece may be rotated while the electrode also is rotated. Or the work may be moved back and forth along a stationary electrode as in a honing operation. What is important is that there be relative motion between the work piece and the electrode, and wherever I refer to a moving electrode I mean to include any means for achieving this relative motion. I,

An important feature of my invention lies in the use of insulating spacers. by which very close spacing between the work piece 17 and 17a and the rotating or moving electrode 10 maybe maintained. The use of insulating spacers in electric removal processes generally (e.g., the electrolytic method, the spark method, and

erated on the work piece will be rough and uneven in contour, sometimes concave, sometimes convex. While this may not be troublesome for some kinds of operations, .it is highly undesirable in making the final finish on ,dies and tools where the surfaces must be smooth and must follow the contour of the electrode. Here it should be understood that while I have, shown an electrode having a flatsurface, there will be many applications in Which the electrode surface will be contoured to produce the desired shape on the work piece.

In the grinding of certain metals and metal carbides, such as tungsten carbide, the abrasive insulating spacers 40, however applied, perform an additional important function which is the removal of an insulating oxide film which forms rapidly under electrolytic action. Since the film is soft, it, may be removed easily and even the lightest direct contact between the work piece and the insulating spacers will bring about this result. But itmust be removed if the electrolytic process is to go forward effectively. p

'If the insulating spacers are made'of hard material, for example diamondparticles, then it is possible to accelerate the rate of material removal by pressing the work piece against the diamond particleswith pressures used the arcmethod) is described in greater detail in my application for United States Letters Patent entitled Improvement in Electric Cutting, Shaping, and Grinding," Serial No. 310,243, and now abandoned.

I prefer to hold a spacing distance under .001 inch and I have obtained good results with a spacing of 10007 inch, but even smaller spacing is permissible down to the point where actual contact between'the work piece and the electrode is likely to occur through any irregularities in the system. The spacing is accomplished by interposing insulating spacers 40 between the electrode and the work 'piece.

I While many means of doing this are available, I prefer to mount the spacers 40 more or less permanently on the surface of the electrode '10-. This may be done for ordinary diamond grinding. Under these conditions the electrolytic removal of material is augmented by abrasive action, with the result that material is removed at a rate approximately 300 percent of the removal rate achieved by diamondgrinding alone, Ordinarily, this augmentation will not be attempted with specialized contouringelectrodes, for normalgrinding pressures produce wear on the diamond particle surface (and removal of diamond particles through chipping, breakage, etc.) so that with time the desired contoured shape is lost and the electrode must be replaced. If grinding pressures are avoided, anclfonly the very light pressure needed for film removal is used, then the electrode and the insulating spacers will have very long life.

Turning now to the electrolyte system; Iuse the system usually provided with grinding machines for supplying coolant to the work area. Thus, as shown in FIG. 1, I provide a sump or supply tank 20, which may be provided with mechanical agitators 20a, a pump 21, a tube or conduit 22, and a nozzle 23 adjacent the work] area. Around the moving electrode I place a shroud 24 which collects the electrolyte'and returns it tothe sump or supply tank 20 through conduit 25. The conduits, of course, should be made of material not readily corroded by the kind of electrolyte used.

As electrolyte, I have used both acid and alkali solutions, but these present some problems because the operator, particularly when doing off-hand grinding, will necessarily be splattered by the electrolyte. On this account salt solutions which are neutral or nearly so, are of some advantage. I have used with considerable success a solution made in the proportion of three ounces sodium nitrate and one and one-half ounces sodium acetate to one gallon of water. While a large variety of conductive electrolyte solutions can be used, I have found that the addition of a salt of the formic acid series, such as sodium acetate, sodium citrate, sodium tartrate, etc., is very helpful in preventing loading up of the electrode in the spaces between the insulating spacers when these are mounted permanently on the electrode.

The flow of electrolyte to the work area itself is aided by the relative motion between the electrode and the material, and by the use of insulating spacers which provide a labyrinth of openings in which electrolyte is entrained and carried into and out of the work area, at the same time being violently agitated. The flow of electrolyte for shaping of ordinary industrial cutting tools should be at the rate of about one liter per minute. In any case, the general flow rate should be adjusted upward until no further increase in current is occasioned by a greater rate of flow. The relative motion between the electrode and the material is not critical when insulating spacers are used, for the insulating spacers are so helpful in carrying electrolyte through the work area that it is not necessary to use extremely high motion. For example, I have varied the speed of rotation of a six inch diameter wheel electrode from 900 r.p.m. to 2400 r.p.m., which speeds are obtainable with the commonly used grinding equipment previously mentioned.

The electrical system represents another important aspect of my invention, for it makes it possible to supply current for the electrolytic process at the maximum level which may be used without causing excessive sparking or arcing through the electrolyte. It is possible, of course, to remove material by sparking or arcing, and some systems have been proposed which depend either entirely or in large part upon sparks or arcs for material removal. I prefer, however, to rely in large measure upon electrolytic action, but if the rate of material removal is to be satisfactory, it is dmirable to use the maximum current which can be carried without breaking over into a degree of sparking or arcing which will be deleterious. The current may, of course, be controlled by a rheo stat which is adjusted manually for with the uniform spacing brought about by the use of insulating spacers, the resistance of the electrolytic circuit will not change very rapidly when a work piece of given size is being shaped. However, one work piece will be different in area from others. Moreover, the resistance path will change as shaping'proceeds, and may change very rapidly in the case of ofi-hand grinding where the work piece is placed in different positions with respect to the electrode. Under these circumstances, manual adjustment for maximum current becomes ,difiicult, and accordingly the tendency is to reduce the current below the maximum that might otherwise be used, thus slowing down the rate of material removal.

The electrical system which I use, when combined with the uniform spacing achieved by use of insulating spacers, gives excellent results, although it may also be of value without the insulating spacers.

The general principle of operation is the use of any alternating current component which arises in the electrolytic circuit as the result of sparking or arcing to provide. a signal for control apparatus which will reduce the supply voltage under these conditions.

While I have used a rectifier system, the same principle of operation may be applied to a motor generator system or to other supply means. If a motor generator system is used, I control the field of the motor generator, reducing the field strength in order to cut down the current supply when serious sparking occurs.

Referring to FIG. 1, I provide a tapped line transformer 82 to accommodate a varietly of available line voltages without the need for a variety of internal circuit components. As shown here, a three-phase system is employed, but it will readily be seen that the same system may be applied to a single phase or a two-phase system by adaptations which will be readily understood.

In the supply lines leading from line transformer 82, I provide saturable iron core reactance coils 84. The main windings have low resistance, and when their iron cores are saturated, pass the line voltage with little loss. The cores are saturated to greater or less degree by bias windings 86, the bias level being adjustable by potenti ometer 122. The current is then passed through voltage reducing transformer and through the rectifier system comprising rectifier elements 92 to the electrolytic circuit proper which consists of supply lines 94, brush 32, movable electrode 10, the electrolyte, the Work piece 17 and 17a, and the tool holder 16. The brush 32 is held by spring 33 against the movable electrode 10. The spring 33 may be mounted on any suitable insulating holder 34. If desired, a plurality of brushes may be used.

In one of the supply lines 94 a shunt resistor 96 is provided across which the control signal is generated.

This control signal is fed to transformer 98 and then amplified by triode 100.

The output of triode 100 is connected through a cathode follower tube 102 to a high pass filter comprising inductance 104, condensers 106 and '108, and resistor 110. The components of this filter are designed to provide sharp attenuation below 1500 cycles per second and minimum attenuation above this frequency. This is done in order that alternating current supply ripple in the electrolytic circuit will not have effect on the control apparatus.

The filtered signal is then passed through transformer 112, germanium rectifier 114, and is partially integrated by condenser 116 and fed from potentiometer 118 to the control grid of pentode 120. Potentiometer 118 adjusts the gain or sensitivity of the control system. Ordinarily,

it is set so as to cause supply voltage attenuation when the slightest incipient sparking is observed between electrode 10 and the work piece 17 and 17a. At this level the sparks appear as fine hair-like strands and contribute little to current conduction or to the removal of material. However, adjustment may be made so as to produce somewhat heavier sparking with some increase in rate of material removal which, however, tends to produce a rough finish on the work piece and causes erosion of the electrode. It may be desired, nevertheless, to operate at this level for rough shaping and then to adjust to a lower level for finishing.

When adjusted at the minimum sparking level, the finish achieved may be as fine, when measured by a Brush analyzer, as five micro inches R.M.S.

The output of pentode 120 is connected to control windings 85 which augment the flux produced by bias windings 86. Normally the output of pentode 120 is suincient to energize control windings 85 to such an extent that a substantial degree of saturation of the iron cores of reactance coils 84 exists. In response to signal, the output of pentode 120 is reduced, thereby reducing the degree .of saturation of the iron cores of reactance coils 84. Under these conditions the eifective inductance increases and the current passed is reduced. The level to which the current falls may be set by the adjustment of potentiometer 122 which controls current supply to bias windings 86. The lower the current supplied to bias windings 86, the lower will be the minimum saturation of iron cores of reactance coils 84, and accordingly, the lower the current 7 will be droppedin response to signal generated by oscillations caused by sparking or arcing. The electric supply system for the control elements just described is a conventional half-wave rectifier system with a voltage doubler circuit for B supply for pentode 120. It consists of transformer 124, rectifiers 1 26 and 128, and condensers 130, 132, and 134.

With space between the electrode and the work piece of the order of .001 inch, a current density of several hundred amperes per square inch is achieved'at voltages between two and thirty volts, which is well within the range of usability without requiring special insulation to protect personnel from seriou electrical shock.

When seen in normal operation, a slight amount of sparking can usually be observed at the trailing edge of the :work piece. The color of the spark will be a pale blue, or may be of reddish cast, or some other cast, de-

pending perhaps upon the electrolyte and the material being worked. This is to be distinguished from arcing, in which a brilliant white-blue light is clearly visible; Frequently the. arc is accompanied with a considerable amount of popping and hissing noise, while such sparking can not be heard above the noise of the machinery and surrounding equipment in a machine shop environment; While arcing under these conditions tends to be somewhat irregular and intermittent, nevertheless the 'arc is characterized by steadier oscillation as seen in an oscilloscope than that produced by sparkin I find that I get best results by adjusting the current supply with relation to the size of insulating spacers used and the size of the work piece, so that some amount of sparking may be seen, but no arcing. For fine finish, but with somewhat slower removal rate, I set the adjustments so that sparking is just barely visible at infrequent intervals. Or the current supply may be limited below the level at which any sparking occurs to give a very fine finish.

The electrolytic action is concentrated almost entirely on the surface of the work piece facing the electrode, but

a very slight amount of material removal also may occur on the surfaces adjoining the surface being'shaped for a distance of as much as l inch back from the surface presented to the electrode. Under some circumstances this is undesirable, and where this is the case I insulate the work piece, for example by lacquer, so that it it electrically insulated on all of the surfacesexcept that toward the electrode. In this way I can obtain very sharp edges. y

In operation, I have been able to remove material from hard substances, such as tungsten carbide, at a rate comparable with the removal rate obtained with the best diamond abrasive practice. The life of the electrodes is very great as neither the electrode nor the insulating spacers need be worn away by substantial grinding pressures. I havealso provided a means of using substances other than diamonds as insulating spacers, thus making it possible to produce lower costgrinding wheels. The surface 8 F the results of this invention may be obtained through the use of substantially the same or equivalent means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Apparatus for supplying and controlling electric current for electrolytic grinding comprising in combination pick-up means responsive to a signal of high-frequency components'arising in the electrolytic circuit of electrolytic-grinding equipment, filter means for rejecting low-frequency components in said signal, means for amplifying said signal, a power source of alternating current, means for rectifying said alternating current to provide a direct-current power source for the electrolytic circuit of the electrolytic-grinding equipment, control means interposed between said power source of alternating' current and said rectifier, and circuit connections from said amplifier to said control means for activating said control means to reduce the flow of current in response to said signal. 7

2. Apparatus. for supplying direct current for electrolytic-grinding equipment comprising in combination a power source of alternating current, a rectifier for converting said alternating current to direct current, current-control means'interposed between said power source and said rectifier, means for activating said current-control means including pick-up means responsive to sparking or arcing in the electrolytic circuit of the electrolyticgrinding equipmenhmeans for amplifying a signal received by said pick-up means, filter means for rejecting ripple frequency components insaid signal, and means for feeding the amplified, filtered signal to said currentcontrol means whereby the flow of current is reduced in response to the. signal.

3. A control system fora rectifier supply of direct current to electrolytic-grinding equipment having an electrolytic circuit, said control system comprising means for receiw'ng a high-frequency signal resulting from sparking or arcing in the electrolytic circuit, means for amplifying and filtering said signal, means for rectifying said signal, and means responsive to said amplified, filtered and rectified signal to reduce direct-current supply vo1tage in response thereto.

4. In apparatus of the type in which a workpiece of hard, electrically conductive material is moved into engagement with a movable electrode having a conductive work face and abrasive elements projecting from the work face a distance not substantially greater than .005", in whichan electrolyte is passed at a rapid flow rate between the workpiece and electrode, and in which an alternating current supply is rectified to apply a direct current: potential across, the workpiece and electrode for removal of material from the workpiece by abrasion and electrolysis, the combination with the supply of an amplifier in the supply controlling the intensity finish on work pieces ground by my apparatus may be made even'be'tter than that ordinarily obtained in cornm mercial diamond abrasive practice.

The entire apparatus is safe and easy for operators of normal skill to use. The whole system and apparatus may be adapted to existing grinding equipment by providing an electrode of the kindhere described and attaching it through an insulating member to an existing grinding spindle, by substituting an electrolyte for the ordinary coolant, and by providing the necessary electrical apparatus in one or more convenient packages.

While a preferred embodiment of thewapparatus for i of the potential applied across the workpieceand electrode, circuit means coupled to the supply selectively responsive to high frequency signals produced by arcing and sparking between the electrode and workpiece to produce a variable intensity control signal as a function of the intensity of the high frequency signals, and means applying the control signal to the amplifier to control the applied potential as an inverse function of the high frequency signal intensity. j

5. In apparatus of the type in which a workpiece of hard, electrically conductive material is moved into engagement with a movable electrode having a conductive work face and abrasive elements projecting from the workface a. distance not substantially greater than .005, in which an electrolyte is passed at a rapid flow rate between the workpiece and electrode, and in which an alternating current supply is rectified to apply a direct current potential acrossthe workpiece and electrode for removal of material from the workpiece by abrasion and eleitmlysis, the combination with the supply of a valve in the supply controlling the intensity of the potential PP 1 I9 iii? workpiece and electrode, circuit means coupled to the supply selectively responsive to high frequency signals produced by arcing and sparking between the electrode and workpiece to produce a variable intensity control signal as a function of the intensity of the high frequency signals, and means applying the control signal to the amplifier to control the applied potential as an inverse function of the high frequency signal intensity.

6. In apparatus of the type in which a workpiece of hard, electrically conductive material is moved into engagement with a movable electrode having a conductive work face and abrasive elements projecting from the work face a distance not substantially greater than .005", in which an electrolyte is passed at a rapid flow rate between the workpiece and electrode, and in which an alternating current supply is rectified to apply a direct current potential across the workpiece and electrode for removal of material from the workpiece by abrasion and electrolysis, the combination with the supply of an amplifier in the supply controlling the intensity of the potential applied across the workpiece and electrode, circuit means coupled to the supply including high pass filter, amplifying, and integrating sections responsive to the high frequency signals produced by arcing and sparking between the electrode and workpiece to produce a unidirectional control signal the strength of which varies as a function of the intensity of the high frequency signals, and means applying the control signal to the amplifier to control the applied potential as an inverse function of the high frequency signal strength.

7. In equipment of the type in which a workpiece of hard, electrically conductive material is moved closely adjacent a movable electrode, in which an electrolyte is passed between the workpiece and electrode, and in which a supply circuit applies a direct current potential across the workpiece and electrode for removal of material from the workpiece by electrolysis, the combination with the supply circuit of signal responsive apparatus controlling the intensity of the applied potential, circuit means responsive to high frequency signals produced by 10 arcing and sparking between the electrode and workpiece to produce a variable intensity control signal as a function of the intensity of the high frequency signals, and means applying the control signal to the apparatus in a manner inhibiting arcing and sparking.

8. In equipment of the type in which a workpiece of hard, electrically conductive material is moved into engagement with a movable electrode having a conductive Work face and insulating elements projecting from the work face a short distance, in which an electrolyte is passed between the workpiece and electrode, and in which a supply circuit applies a direct current potential across the workpiece and electrode for removal of material from the workpiece by electrolysis, the combination with the supply circuit of signal responsive apparatus controlling the intensity of the applied potential, circuit means responsive to high frequency signals produced by arcing and sparking between the electrode and workpiece to produce a variable intensity control signal as a function of the intensity of the high frequency signals, and means applying the control signal to the apparatus in a manner inhibiting arcing and sparking.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Keeleric: Steel, March 17, 1952, vol. 130, No. 3, pp. 84 to 86.

New Processes For Machining and Grinding, Report No. MAB-IS-M of National Research Council,

January 18, 1952, appendix VI, PP. 1-9. 

1. APPARATUS FOR SUPPLYING AND CONTROLLING ELECTRIC CURRENT FOR ELECTROLYTIC GRINDING COMPRISING IN COMBINATION PICK-UP MEANS RESPONSIVE TO A SIGNAL OF HIGH-FREQUENCY COMPONENTS ARISING IN THE ELECTROLYTIC CIRCUIT OF ELECTROLYTIC-GRINDING EQUIPMENT, FILTER MEANS FOR REJECTING LOW-FREQUENCY COMPONENTS IN SAID SIGNAL, MEANS FOR AMPLIFYING SAID SIGNAL, A POWER SOURCE OF ALTERNATING CURRENT, MEANS FOR RECTIFYING SAID ALTERNATING CURRENT TO PROVIDE A DIRECT-CURRENT POWER SOURCE FOR THE ELECTROLYTIC CIRCUIT OF THE ELECTROLYTIC-GRINDING EQUIPMENT, CONTROL MEANS INTERPOSED BETWEEN SAID POWER SOURCE OF ALTERNATING CURRENT AND SAID RECTIFIER, AND CIRCUIT CONNECTIONS 